Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!munnari.oz.au!brahma!summer
From: summer@brahma.trl.oz.au (Mark Summerfield - Switching)
Newsgroups: comp.realtime
Subject: VxWorks ethernet output
Message-ID: <7152@munnari.oz.au>
Date: 25 Mar 91 05:13:51 GMT
Sender: news@cs.mu.oz.au
Reply-To: m.summerfield@trl.oz.au
Organization: Telecom Research Laboratories, Melbourne, Australia
Lines: 27

I have an annoying problem with VxWorks' etherOutput() function 
(VxWorks running on a Motorola MVME-147S CPU board). As part
of a LAN bridging system, I need to transmit packets with arbitrary
source addresses. If I use etherOutput() to do this, the interface's
output routine (I assume) replaces the contents of the source address
field with the address of the CPU board that VxWorks is running on.

I have a workaround, which involves adding an output hook routine
(with etherOutputHookAdd()) which inserts the desired source address
(it seems that the hook routine is called after the replacement, directly
before the packet is transmitted). This wastes time, space (admittedly
not much) and requires a really shabby trick of storing a pointer
in the destination address field so that the correct packet header can
be found by the hook routine.

In short, I don't like it, and hope that there's a better way! The
situation is possibly complicated by the fact that I want the VxWorks
network interface to continue to function normally as well. Has
anybody successfully tackled this problem before?

Thanks in advance for any help,

Mark.
------------------------------------------------+-----------------------------+
Mark Summerfield, Telecom Research Laboratories | "A witty saying proves      |
ACSnet[AARN/Internet]: m.summerfield@trl.oz[.au]|       nothing." -- Voltaire |
Snail: PO Box 249, Clayton, Vic., 3168          +-----------------------------+